The invention relates to an internal-combustion engine comprising an intake system which consists of a chamber with an intake connection and individual suction pipes which are connected with a cylinder head and which lead into the individual cylinders by means of valves, an air supply and air purification system being connected with the intake connection.
Because of a variable air flow rate to the individual cylinders in the cylinder head, airborne noises occur in an intake system of an internal-combustion engine which are transmitted to the outside by way of the chamber of the system and other components and represent an acoustic deterioration of the comfort.
It is an object of the invention to provide an internal-combustion engine comprising an intake system in which a reduction of airborne noises is carried out.
According to the invention, this object is achieved by an arrangement wherein an air guiding pipe is connected with the intake connection of the chamber, which air guiding pipe projects freely into the chamber by way of a pipe connection and is arranged coaxially with respect to this pipe connection, the mouth opening of the air guiding pipe extending in a plane which extends between the two individual suction pipes and has an identical distance from the center axes of the individual suction pipes of a second and third cylinder of the internal-combustion engine.
For reducing airborne noises, an air guiding pipe is provided in the chamber of the intake system which, on the inlet side, is fastened to the intake connection of the chamber and projects freely into the chamber. This chamber ensures a distributed charging of the cylinders because of the essential separation of the connections by the volume of the chamber. On the other hand, the mutual independence of the wave effect in the individual suction pipes of the cylinders results in a more defined development of the gas-resonance vibrations in each individual suction pipe.
Because of the asymmetry of the acoustic loads generated by the chamber, the loads on the individual suction pipes of the individual cylinders will differ and there will be a lower non-match of the resonance frequency in the separate individual suction pipes. Therefore, the resonance vibrations (on their resonance frequency), which arise in one of the cylinders, are not damped by the vibrations which occur in the chamber as a result of the individual suction pipes and even when the starting pulses are compensated by the cylinders. The reason is that they move in antiphase. The second unfavorable phenomenon is connected with the excitation of the first asymmetrical form of the gas vibrations in the chamber. Their frequency is regularly close to a natural frequency of the gas vibration in the individual suction pipe, which leads to an intensive sound radiation from the system, particularly on the frequencies which coincide with the non-linear harmonic of the primary frequency of the intake process.
For eliminating this disadvantageous phenomenon, an air guiding pipe is inserted into the chamber which is arranged coaxially to a center axis with the center axis of the chamber space and, on the inlet side, is fastened in the intake connection of the chamber. This intake connection connects the chamber with the air supply and air purification system.
The mouth opening of the air guiding pipe provided in the chamber is situated in a plane which is arranged perpendicularly to the lateral wall of the chamber and which has approximately the same distance from the center axes of the individual suction pipes of the second and third cylinder.
The free end of the air guiding pipe may be partially perforated or have radial flow-through openings.
The presence of an air guiding pipe arranged in a certain manner has the result that the acoustic load on the cylinders which operate in antiphase is symmetrical and eliminates the asymmetrical excitation in the lowest frequencies.
In addition, the mouth opening of the air guiding pipe is situated in the proximity of a node (crossover) of a first natural gas vibration of the chamber of the intake system. As a result, it is also prevented in the case of a resonance excitation that a transmission of the acoustic energy takes place by means of the air guiding pipe in the direction of the inlet mouth and therefore to the environment.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.